The invention concerns a method and apparatus for decomposing supersaturated sodium aluminate liquors, without agitation, the liquors being designed for the production of alumina by the BAYER process, which is the essential method of producing alumina chiefly for conversion to aluminum by high temperature electrolysis of a fused electrolyte. By this process the bauxite is treated with a hot aqueous sodium hydroxide solution at an appropriate concentration, thus making the alumina soluble and producing a supersaturated sodium aluminate solution. When the solid phase which constitutes the unattacked residue of the ore (red mud) has been separated, the supersaturated sodium aluminate solution is seeded with aluminum hydroxide, which acts as a trigger to bring about precipitation of the aluminum trihydroxide.
This operation, which is commonly described as "decomposition" in the art, generally takes place in several successive stages, which are distinguished chiefly by the temperature, particle size distribution and quantity of seed introduced, the arrangement for circulating the liquors in the successive tanks and possible recycling steps.
All industrial installations for making alumina by the BAYER process operating in the world to this day use agitated decomposers. Every precaution is taken in construction and utilization to avoid any stoppage of the agitation and circulation of the liquors, since this would result in an irreversible deposit of alumina trihydrate in the bottom of the tanks and the need to empty and chemically unblock them.